<template>
  <div>
    <h1>ComTest组件</h1>
    <div>a: {{ a }}</div>
    <button @click="$emit('update:a', 200)">update:a</button>
  </div>
</template>
<script>
export default {
  props: {
    a: {
      type: Number,
      required: true
    }
  }
}
</script>
